I'm looking at a 1999 Trek 5500 frame with an ahead stem. Is it possible to change this to a quill stem? if not, why not?

I have been told that in some weird way, these older versions of this frame could be installed with either ahead or quill. But I asked someone who had his for sale, mounted with an ahead stem, whether it could be exchanged for a quill, and he said "yes, but you need a new fork?" - no further explanation. How does the fork matter in this?

Thanks in advance. The specs catalog from 1999 doesn't offer an explanation. It only says the fork is an ICON Air Rail, and shows a diagram of the head cups installation.

The short version:
No, they're not interchangeable.
Quill stems rely on the top half of the headset to set and hold the headset bearing preload.
And you can only do that with threaded forks that take threaded headsets.

For aheadset/threadless, headset bearing preload is set and held by Star fangled nut/compression plug + top cap + stem. And you can't get that functionality from a quill


The long version:
With a quill stem, the steerer tube of the fork is threaded at the top, and protrudes just far enough past the top of the headtube of the frame to make room for the top headset assembly. The top headset assembly has a cup that's pressed into the headtube, then a cone that's threaded onto the steerer tube and then a locknut on top of that.

(Maybe a washer or two, but lets ignore them at the moment)

The threaded parts, cone and locknut, is what sets the bearing preload.

The quill (stem) is then inserted into the steerer tube and locked in place by a sliding wedge at the tip of the quill. You can pull the stem out w/o interfering with the headset bearing preload.


With a threadless/aheadset stem, the steerer tube is smooth, and extends well above the top headset assembly.
The top headset assembly is also smooth. It centers the steerer tube in the headtube, but doesn't really grip it with any important amount of force.
Headset only has not chance of setting or holding the headset bearing preload.
Then the stem is placed over the steerer tube (add spacers as needed/preferred). Bearing preload is set by the stem being forced downwards courtesy of the top cap and an anchor inserted into the end of the steerer tube. Usually something called a star fangled nut, but there are other options available.
Then the wraparound part of the stem is tightened around the steerer tube to lock the preload in.

So, if you were to try to use a quill stem in a threadless fork, there's no way to set the headset bearing preload any more. There is no mechanism allowing a quill stem to be pulled down, while bracing against the top headset assembly.

If you really insist, there are workarounds.
It's possible to set the preload by external means. Big C-clamp, threaded rod through steerer etc etc, then use a properly sized seatpost clamp around the steerer tube to lock the preload in.
If your steerer tube can take the expansion force caused by the wedge, you can then install a quill stem and ride happily ever after.

But why?

The only practical advantage of quill stems is that they allow for greater/easier adjustability of bar height.

And unless it's a loaner, bike, people tend not to touch that adjustment very often.

Thank you for your answer. I think I understood most of it. I have both bike with aheadset stems and quill stems.

The reason is that I'm making an exact replica of Lance's 1999 Tour de France bike. And he was using a Cinelli Oyster quill stem on his Trek.

If I understand you correctly, then Trek has been selling these frames with two different forks? Otherwise it wouldn't be possible. I'm asking mainly because I would hate to buy a Trek bike with an aheadset stem, in the perception that I could exchange it, just to figure out I need to source a different fork.

ZWhether Trek sold them as that, or if it was a special team/rider adaptation, I have no idea. Some say threadless forks can be threaded. But two different forks seems like the most probable explanation. The frame doesn't care, it can deal with either easily enough. But for a slick installation, the steerer tubes of the forks, and the (top half of the) headset has to be different.
The external preload-and-seat post clamp fix would work. And would PROBABLY allow you to use a quill stem. But it wouldn't be an exact replica as you'd be using the wrong headset.

Thank you. I'm starting to understand the different components now. Looking at the catalog of the frames for that year. It seems as though the frameset only (US Postal colours), was sold with the intention of using a quill stem?, as far as I can see from the photo. But on the top photo, the complete bike, black one, it is fitted with an aheadset stem.

I'm going to sound like an idiot, but would they be fitted with two different forks?

Yes, the postal colors frame uses a threaded fork while the black one uses a threadless fork. I have no idea why Trek would do this, but that was right around the time when they were switching over to threadless.

Yeah.
The only way to make slick installations with either quill or threadless stems is to use different forks. Or for a greater degree of accuracy - with different steerer tubes. With their matching headset parts.

Workarounds do exist, but I can't think of a bike being made from scratch that way.

Trek has a history of going back and forth on individual features from production year to production year.

For the 1993 Model Year, Trek switch the 2300 composite frame from thread (earlier models) to 1" threadless headsets). As far as I could tell, other Trek composite bikes still had 1" threaded headsets. The next year (1994), the Trek 2300 came with a threaded 1" headset, continued to use the threaded headset until 1997/1998 when the composite bikes were discontinued.

The 1994 Trek 1400 that I have came with a 8-speed RX100 group. The next year Trek downgraded to 7-speeds on the Trek 1400. The 1997 (last year of the bonded aluminum frame) Trek 1400 that I have came from Trek with a 7-speed RSX group.

I don't think I've ever see a Trek model that Trek offered both threadless and threaded headsets on the same model year.

I don't have any of Trek's all carbon frames, but I do have Trek steel, aluminum, and composite frames. Seems to me that if you want a Trek 5200 with a quill stem, what you need to do is study Bikepedia to see which model years came with quill stems, and limit your search to bikes of the particular model and model year that featured quill stems. Keep in mind that the 5000, and 5500 models from the same model year, may not carry the same type of headset.

I got a Trek 99' OCLV frame home with a threadless setup. It turns out that this particular frame/fork combination is a form of hybrid. The fork legs are carbon, but the steerer tube is a 1'' steel one, with no threads. There is a sliced shim or sleeve around the steerer tube to make the aheadset stem fit with spacers.

In other words, it's intended for a quill stem, and the only thing missing is to have the local shop cut the threads.